1. Field of the Invention
The subject of the present invention is a lighting and/or signalling device for motor vehicles, comprising at least one optical guide capable of producing a scattering of the light over at least part of its length. The invention also relates to a vehicle comprising such a lighting or signalling device.
2. Description of the Related Art
In the field of lighting and of signalling for motor vehicles, the use of optical guides is becoming more widespread. An optical guide is, very schematically, an oblong element made of transparent material, generally in the form of a cylinder or of a flat slice. Near to one of the ends of the guide, referred to as the entry face of the guide, one (or more) light sources is disposed, for example a small light source of the light-emitting diode type: the light rays emitted by this source propagate by total internal reflection within the length of the guide in the direction of its opposite end, referred to as terminal face of the guide. A part of the light rays propagating within the guide will exit from it by the face referred to as front face of the guide due to the presence of reflecting elements disposed on the face referred to as back face of the guide, opposite to the preceding one. These reflecting elements are for example composed of prisms. The guide thus emits light over its whole length. They have the advantage of being able to take very varied geometric shapes, rectilinear or rounded, notably according to an arc of a circle, and provide a lighting surface even in regions that are virtually inaccessible to a headlamp or to a light of the vehicle. It thus contributes significantly to the style of the headlamp or of the light. However, the existing light guides are imperfect. Indeed, it is often difficult to ensure an identical level of illumination between the first and the second end of the guide, especially if it has a significant length, the level of Illumination tending to decrease with the distance from the entry face of the guide. Furthermore, it is also difficult to ensure a uniform aspect to the guide for any viewing angle with respect to the guide, the light exiting from the guide having an angular distribution that is often not broad enough. In fact, this is an important point depending on the disposition of the guide and its shape inside of the headlamp or of the light: the guide tends to be designed such that it mainly Illuminates along the axis of the vehicle in order to comply with photometric standards. However, it also turns out to be important to have a uniformly lit aspect that is also visually pleasing when the observer moves away from the longitudinal axis of the vehicle. It may also be desirable to improve the optical efficiency of the guide, because there can be leaks of light lost notably through the back face of the guide.
A solution already known from the Patent EP 1 443 265, which is equivalent to U.S. Patent Publication 2004/0184286 and U.S. Pat. No. 7,104,678, which are incorporated herein by reference and made a part hereof, is to associate with a light guide a reflector situated at the back of the light guide, in order to limit as far as possible the leaks of light and to thus improve the optical efficiency of the guide. The Patent application WO 02/40 917, which is equivalent to U.S. Patent Publication 2002/0114168 and U.S. Pat. No. 6,637,924, which are incorporated herein by reference and made a part hereof, discloses a vehicle signalling device in which a reflecting layer is disposed by bonding against a reflection face of an optical guide.
Finally, a solution is known from the document EP1775511, which is equivalent to U.S. Patent Publication 2007/0121334 and U.S. Pat. No. 7,726,854, which are incorporated herein by reference and made a part hereof, where a diffusing screen is disposed on the back of a light guide so that a part of the light rays escaping through the reflection face of the optical guide are at least partially returned into the guide.
These guides are generally used to produce a light function in an overall direction of light beam exiting from the lighting and/or signalling device. However, in this type of lighting and/or signalling device, few light rays reach the sides and the device appears to be extinguished.